A5038578153- Geology and Paleoclimatology Research
- Isotope Analysis in Ecology
- Marine and coastal ecosystems
- Methane Hydrates and Related Phenomena
- Marine Biology and Ecology Research
- Oceanographic and Atmospheric Processes
- Atmospheric and Environmental Gas Dynamics
- Groundwater and Isotope Geochemistry
- Ocean Acidification Effects and Responses
- Cryospheric studies and observations
- Landslides and related hazards
- Paleontology and Stratigraphy of Fossils
- Management and Marketing Education
- Marine and environmental studies
- Astro and Planetary Science
- Microbial Community Ecology and Physiology
- Geological formations and processes
- Marine Bivalve and Aquaculture Studies
- Geochemistry and Elemental Analysis
- Geological Studies and Exploration
- Coral and Marine Ecosystems Studies
- Carbon Dioxide Capture Technologies
- Advanced Chemical Sensor Technologies
- Education Systems and Policy
- Cardiac Valve Diseases and Treatments
University of California, Irvine
2014-2024
University of South Florida
2024
College of Marin
2024
University of South Florida St. Petersburg
2024
Irvine University
2018-2023
Philips (United States)
2017
Princeton University
2011-2016
Scripps Institution of Oceanography
2011-2012
University of California, San Diego
2011-2012
Abstract. A major impediment to understanding long-term changes in the marine nitrogen (N) cycle is persistent uncertainty about rates, distribution, and sensitivity of its largest fluxes modern ocean. We use a global ocean circulation model obtain first 3-D estimate denitrification rates that maximally consistent with available observations nitrate deficits isotopic ratio oceanic nitrate. find rate suboxic waters sediments 120–240 Tg N yr−1, which lower than many other recent estimates. The...
[1] The difference between nitrate δ15N and δ18O, or Δ(15–18), is sensitive to organic matter remineralization tracks the modification of as it passes from deep Pacific Ocean, through Southern Ocean surface, into intermediate-depth Pacific. Circumpolar Deep Water (CDW) upwelled with a Δ(15–18) +3.0‰ appears unaltered by assimilation in Antarctic surface. However, within Subantarctic Mode (SAMW)—the primary conduit deep-sea nutrients lower latitudes—nitrate δ18O are both higher than CDW,...
Abstract Ocean circulation supplies the surface ocean with nutrients that fuel global productivity. However, mechanisms and rates of water nutrient transport from deep to upper are poorly known. Here, we use nitrogen isotopic composition nitrate place observational constraints on Southern into pycnocline (roughly 1.2 km), as opposed directly ocean. We estimate 62 ± 5% phosphate originate Ocean. Mixing, advection, accounts for most gross input pycnocline. in net, mixing carries away Despite...
Using new and published marine fossil radiocarbon (14C/C) measurements, a tracer uniquely sensitive to circulation air-sea gas exchange, we establish several benchmarks for Atlantic, Southern, Pacific deep-sea ventilation since the last ice age. We find most 14C-depleted water in glacial bottom depths, rather than mid-depths as they are today, which is best explained by slowdown overturning addition "flipped" configuration. These observations cannot be produced changes exchange alone,...
Abstract We report nitrogen (N) isotopic measurements of nitrate, total dissolved nitrogen, and particulate from Antarctic pack ice in early late spring. Salinity‐normalized concentrations fixed N are approximately twofold higher than seawater, indicating that sea exchanges with seawater after its formation. The production low‐ δ 15 immobile organic matter by partial nitrate assimilation the subsequent loss high‐ during brine convection lowers relative to winter‐supplied nitrate. effect...
Equatorial Pacific nitrate 15N/14N and 18O/16O (δ15N δ18O) measurements from repeat station occupations are used to: (1) identify the source of surface waters, (2) estimate assimilation isotope effect, (3) characterize temporal relationship between supply consumption in (4) quantify degree nitrate-bearing waters. Surface was consistent with a closed pool at 63–80% stations. Those stations yielded effects 6.0‰ ± 0.4‰ for N 5.9‰ 0.6‰ O, an N:O effect ratio 1.0 0.1, being dominant...
Enhanced overturning circulation in the glacial North Pacific caused warming, nutrient limitation, and lower atmospheric CO 2 .
Abstract The greater Agulhas Current region is an important component of the climate system, yet its influence on carbon and nutrient cycling poorly understood. Here, we use nitrate isotopes (δ 15 N, δ 18 O, Δ(15–18) = N–δ O) to trace regional water mass circulation investigate nitrogen in adjacent recirculating waters. deep intermediate waters record processes occurring remotely, including partial assimilation Southern Ocean denitrification Arabian Sea. In thermocline surface, tropically...
We report measurements of the nitrogen isotopic composition nitrate (the δ 15 N NO 3 − ) across equatorial Pacific, for zonal transects from 165°E to 95°W and meridional 95° 110°W. The is similar in thermocline (≈100 m) intermediate depth waters (≈150 600 m), averaging (7.1 ± 0.3)‰ 0.1)‰, respectively. These values are more than 2‰ higher subthermocline Southern Atlantic Oceans ≈1‰ putative source high latitude South Pacific (Subantarctic Mode Water, SAMW). combined constraints concentration...
Abstract Nitrate persists in eastern equatorial Pacific surface waters because phytoplankton growth fueled by nitrate (new production) is limited iron. isotope measurements provide a new constraint on the controls of concentration this region and allow us to quantify degree temporal variability consumption. Here we show that consumption these cannot be solely external supply iron waters, which occurs upwelling dust deposition. Rather, substantial fraction must supported recycling within...
Abstract To investigate the controls on N 2 fixation and role of Atlantic in global ocean's fixed nitrogen (N) budget, is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed 15 N/ 14 differences between northward southward transported nitrate. inputs 27.1 ± 4.3 Tg N/yr 3.0 0.5 are estimated north 11°S 24°N, respectively. That is, ~90% occurs south 24°N a region upwelling that imports phosphorus (P) excess relative to...
Abstract. Nitrate is a critical ingredient for life in the ocean because, as most abundant form of fixed nitrogen ocean, it an essential nutrient primary production. The availability marine nitrate principally determined by biological processes, each having distinct influence on N isotopic composition (nitrate δ15N) – property that informs much our understanding cycle well ecology, fisheries, and past conditions. However, sparse spatial distribution δ15N observations makes difficult to apply...
Abstract Biological productivity in the ocean directly influences partitioning of carbon between atmosphere and interior. Through this cycle feedback, changing has long been hypothesized as a key pathway for modulating past atmospheric dioxide levels hence global climate. Because phytoplankton preferentially assimilate light isotopes major nutrients nitrate silicic acid, stable (C), nitrogen (N), silicon (Si) seawater marine sediments can inform on nutrient cycling, by extension relationship...
There is little agreement among models in predicting the average state of tropical Pacific when subjected to enhanced greenhouse gas forcing. This uncertainty emphasizes importance reconstructing past variability climate through episodes significant and estimable radiative Thus far, efforts along these lines have concentrated primarily on inferences sea surface temperature from deep‐sea sediments. Here we offer a different view equatorial over ∼1.2 million years (Myr)—before after...
As companies begin selling credits for marine carbon dioxide removal in largely unregulated marketplaces, scientists must develop standards assessing the effectiveness of methods.
Abstract The Southern Ocean regulates atmospheric CO 2 and Earth's climate as a critical region for air‐sea gas exchange, delicately poised between being source sink. Here, we estimate how long water mass has remained isolated from the atmosphere utilize 14 C/ 12 C ratios (Δ C) to trace pathway escape route of carbon sequestered in deep ocean through mixed layer atmosphere. position our core at northern margin Indian Ocean, tracks latitudinal shifts frontal zones across deglaciation. Our...
Abstract Subsurface waters from both hemispheres converge in the Western Equatorial Pacific (WEP), some of which form Undercurrent (EUC) that influences equatorial productivity across basin. Measurements nitrogen (N) and oxygen (O) isotope ratios nitrate (δ 15 N NO3 δ 18 O ), dissolved inorganic carbon 13 C DIC complementary biogeochemical tracers reveal northern southern WEP have distinct histories. Organic matter remineralization plays an important role setting nutrient characteristics on...
Gas exchange between the atmosphere and ocean interior profoundly impacts global climate biogeochemistry. However, our understanding of relevant physical processes remains limited by a scarcity direct observations. Dissolved noble gases in deep are powerful tracers air-sea interaction due to their chemical biological inertness, yet isotope ratios have remained underexplored. Here, we present high-precision gas elemental from North Atlantic (~32°N, 64°W) evaluate parameterizations using an...
Abstract. For over a decade, oceanographers have debated the interpretation and reliability of sediment microfossil records indicating extremely low seawater radiocarbon (14C) during last deglaciation – observations that suggest major disruption in marine carbon cycling coincident with rising atmospheric CO2 concentrations. Possible flaws these include poor age model controls, utilization mixed infaunal foraminifera species, bioturbation. We addressed concerns using glacial–interglacial...
Here we present new results on the sedimentation rates and vertical mixing in deep-water region (966–3741 m) of southern Gulf Mexico, from a collection 42 cores retrieved continental slopes abyssal plain. These were dated with aid accelerator mass spectrometry (AMS) 14C determinations planktic foraminifera. We applied Modified Mixing Box Model (MMBM) to evaluate mean (Sm), estimate age surface sediments (T0) that result processes. Sm range between 5 9 cm kyr−1 plain slopes, highest are...